This invention relates to a self-contained Energy Storage and Recovery System (ESRS) device for use in a vehicle, and specifically to an ESRS device comprising a high speed flywheel, i.e. a flywheel which can run at speeds greater than 20,000 revs, such as that disclosed in the Applicant's Patent No. GB2449117.
Currently known mechanical ESRS devices comprise a Continuously Variable Transmission (CVT) to transfer torque between the flywheel and the vehicle. The efficiency of torque transfer in a CVT-based ESRS device is dependent upon power, and only exhibits a high efficiency at high power levels.